When a rotor shaft mounted in bearings has not been rotated for a period of time, the oil film between the rotor shaft journal and the lower bearing surfaces becomes extremely thin or nonexistent. Metal-to-metal contact between the shaft journal and the lower bearing surfaces sometimes occurs in view of the weight of the rotor shaft, e.g., on the order of 20 or more tons, on the lower bearing surfaces. The reduced oil film or metal-to-metal contact between the rotor shaft journal and the lower bearing surfaces results in an inability to rotate the rotor shaft at start-up in the absence of a very high breakaway torque applied to the shaft. Apart from the undesirability of a high breakaway torque, it causes problems in routine maintenance of the shaft and bearings. For example, the lower bearings cannot be removed because of the weight of the shaft resting on those bearings. Additionally, even if the shaft is jacked up, most jacking-type devices do not permit the shaft to rotate for maintenance purposes while elevated off the lower bearing surfaces.
These problems, to some extent, have previously been recognized. Systems exist to facilitate initial rotation and start-up of a generator rotor shaft. For example, hydrostatic systems employing high-pressure oil feeding through the lower bearing surfaces have been used to essentially raise the shaft journal from the bearing sufficiently to permit the formation of an oil film between those surfaces, whereby the rotor shaft can be readily rotated with minimum starting torque. Such hydrostatic systems, however, involve complicated bearing structure, including the necessity to route high-pressure oil through passages and orifices in the bearings and bearing surfaces. Furthermore, such high-pressure oil systems cannot be used in routine maintenance, particularly, when the upper bearing surfaces have been removed. Thus, this added expense and complexity does not cure both start-up and maintenance problems. Other types of devices for lifting the rotor from the bearing such as jacks or wooden cribbing have also been used. Use of these, however, is oftentimes awkward and dangerous.